1. Field of the Invention
This invention relates to pumps and, more particularly, to a novel and highly-effective high-lift pump adapted to pump liquids from locations that are deeply recessed and accessible only via narrow openings--for example, openings having a width of less than an inch.
2. Description of the Prior Art
The gravitational field of the earth interacts with the earth's atmosphere to produce an atmospheric pressure of about 14.7 pounds per square inch at sea level. In other words, a column of air having a cross section of one square inch and extending from sea level to the outer limit of the atmosphere weighs about 14.7 pounds. The pressure of one atmosphere will support a column of liquid to a height such that the pressure at the bottom of the column of liquid is equal to one atmosphere. If a nearly perfect vacuum is maintained above the column of liquid, the columnar height is about 32 feet in the case of water, which has a specific gravity of 1.0. Even at sea level, it is therefore not possible, using only a vacuum, to pump water to a height greater than about 32 feet. Moreover, if a sump line is connected at a height of, say, 30 feet in a system using only a vacuum, the rate of discharge into the sump line will be very low under the best circumstances.
Of course, it is possible by means of positive pressure to pump water to any height. However, positive-pressure pumps of high capacity are conventionally large, often a foot or more in diameter. This precludes their use to pump water from locations that are deeply recessed and accessible only via openings too narrow to admit such pumps. For example, conventional positive-pressure pumps are not satisfactory for use in pumping out primary-side water from the lower head connected to the lower ends of steam generator tubes of a single-pass team generator of a large power station.
Air-lift pumps are also known and are disclosed in Lionel S. Marks, Standard Handbook for Mechanical Engineers, 7th ed. (New York: McGraw-Hill Book Company, 1967), section 14, pp. 19-20. In an air-lift pump, an air pipe delivers air to the bottom of a drop pipe inserted for example into a water well and forms a mixture of water and air in the drop pipe that is less dense than the unaerated water in the well. Consequently, the mixture rises in the drop pipe to a level higher than the level of the surrounding water. This process requires a high throughput of air and is relatively inefficient. Moreover, the pumping height that can be achieved is limited by the "submergence" of the pump, which is defined as the difference between the level of the water in the well and the level at which the air enters the drop pipe. For example, for a lift of 25 feet, a submergence of 100 feet is required, and for a lift of 100 feet, a submergence of 200 feet is required. In many environments (e.g., in the lower head connected to steam generator tubes of a single-pass steam generator of certain large power stations), such a large submergence is impossible to achieve.
The broad concept of employing a vacuum to raise a column of water to height supportable by one atmosphere and then applying pressure to the column of water to pump it to a greater height has been known at least since 1847, as evidenced by a U.S. Pat. No. 5,179 to Winder. The Winder patent discloses the use of a pair of bulky airtight cylinders. One of these cylinders is lowered into a well as illustrated in the patent but would be quite impractical for use in pumping out primary-side water from the lower head connected to single-pass steam generator tubes of a large power station.
The same general principle has been applied over the years in various apparatus. U.S. Pats. Nos. 47,034 to Pease, 1,060,826 to De Hymel, 1,778,723 to Oeder, 2,777,399 to Clark, and 2,976,814 to Ver Planck et al. all disclose apparatus for pumping water or oil from a well using alternating vacuum and pressure. A U.S. Pat. No. 3,310,002 to Wilburn discloses the use of a similar principle in laboratory apparatus, and a U.S. Pat. No. 3,861,830 to Johnson and a U.S. Pat. No. 4,640,322 to Ballester disclose apparatus using a similar principle and specially designed to pump dry bulk products (Johnson) or a pulverulent material that behaves as a fluid en masse (Ballester).
The devices disclosed in the prior art are relatively complicated. The above-mentioned patent to Oeder, for example, discloses apparatus that depends on two check valves. A first valve is open and a second valve closed during the suction stroke, and the first valve is closed and the second valve open during the pressure or ejection stroke.